The invention relates to a chair, in particular an office chair, comprising a vertical base starting out from a bottom part, a seat plate which is pivotally connected about a first horizontal transverse axis to a forwardly directed support arm of the base, and a bar receiving the back rest, which bar is connected swingably about a second horizontal transverse axis to the base and is connected swingably through a third horizontal transverse axis to the rear area of the seat plate, which latter axis at the same time permits a relative movement between the bar and seat plate perpendicularly to the third transverse axis.
Chairs with a chair mechanism of the described type are known in various designs. The front end of the seat plate and the lower end of the bar are in all cases connected pivotally to the base or its support arm, and the rear end of the seat plate is connected to the bar of the back rest in a slide bearing, which at the same time permits a swinging movement. The swinging movement of the seat plate is in such chair mechanism forcedly coupled with the one of the back rest. However, the back rest covers a larger angle of swing than the seat plate. This corresponds with the ergonomic needs of the user during an adjustment of the chair between an erect working position and a leaning-back rest position. Regarding the state of the art, reference is made to German Nos. GM 77 11 865, AS 28 22 574, OS 29 04 148 and European Patent No. 014 001.
Furthermore, it is generally known for chairs of the mentioned type and others to have a spring act against the adjustment in the leaning-back rest position. Since the forces which are to be absorbed by the spring are significant, it is relatively difficult to find a spring which is, on the one hand, sufficiently large in order to be able to absorb the forces and is, on the other hand, substantially nonvisible and can be stored in the usual casing on the underside of the seat plate. Thus, for example, according to German No. GM 77 11 865, a gas pressure spring is provided behind the back rest, which requires an additional rear casing for the back rest. In other constructions, the occurring forces are distributed onto several smaller springs so that a considerable structural input is needed. U.S. Pat. No. 2,321,385, which must also be mentioned in the present case, provides a compression spring which lies freely in front of the base and which not only influences the appearance of the chair but also presents a danger regarding injury.
Therefore, the basic purpose of the invention is to produce a chair of the type of this class, in which the problem of the springy support of the seat plate and of the back rest is solved in a structurally simple and yet strong and sturdy manner.
This purpose is attained inventively by a torsion spring with at least one spring arm which is angled from the torsion axis, which torsion spring is supported with its torsion axis parallel to the first horizontal transverse axis fixed against rotation on the support arm or the base, which spring arm extends under the rear area of the seat plate and is there supported in a support bearing on the underside of the seat plate and a slide bearing on the bar.
The rearwardly directed arm of the torsion spring serves thus at the same time to support the rear side of the seat plate and serves the movable and swingable connection of the seat plate to the bar. With this a double function is met, which s far required on the one hand a swivel and slide bearing between the seat plate and bar, and on the other hand a separate fastening of the spring. From this results a significant structural simplification. Furthermore, combining two functions results in saving space, which makes it possible to store the spring with the bearings on the seat plate and the bar in a relatively flat casing on the underside of the seat plate.
Since not only a sliding movement but also an, even though slight, swinging movement occurs between the rear end of the seat plate and the bar, the invention offers the further advantage that in the inventively chosen arrangement by bending the rear end of the spring and/or by deforming a slide bearing, which consists for example of elastic plastic material, this swinging movement is made possible. The slide bearing can, moreover, also be constructed such that it permits a tilting movement of the spring.